NAXJA Forums -::- North American XJ Association  

Go Back   NAXJA Forums -::- North American XJ Association > NAXJA Unibody Jeep Technical Forums > Jeep Cherokee XJ (1984 - 2001) > OEM Tech Discussion
HOME Member FAQ Sponsor Info Rules Bylaws E-Mail

OEM Tech Discussion Forum for OEM (Original Equipment) or stock XJs and MJs.

Reply
 
Thread Tools Display Modes
  #1  
Old January 4th, 2022, 07:13
Lost_Wrench Lost_Wrench is offline
NAXJA Forum User
 
Join Date: Dec 2020
Location: CO
Posts: 95
Fuel Pump Check Valve or leaky Injectors?

My 96' XJ is taking too long to start at times and the symptoms seem backwards from most people's issues with check valves and leaky injectors. If the Jeep has been sitting overnight or long enough for the engine to be cold, it fires right up on the first try but then shakes and stumbles for a minute or so (or until I give it some gas) before idling smoothly. Once the motor has started and warms up though, it takes 2-4 crank/prime cycles to start and it seems to be slowly worsening over time. Isn't this backwards from most check valve issues where people have to prime the key several times after its been sitting due to the fuel in the fuel line slowly draining back into the tank?

This Jeep runs great otherwise, no check lights or trouble codes. About a year and half ago (approx 5k miles ago) it got a new fuel tank, fuel pump, and fuel filter.
Reply With Quote
  #2  
Old January 4th, 2022, 07:53
RCP Phx RCP Phx is offline
NAXJA Forum User
 
Join Date: Mar 2003
Location: Phoenix,Az
Posts: 15,753
Re: Fuel Pump Check Valve or leaky Injectors?

Sounds like the injectors going bad, get a new "matched" set and be done.
Reply With Quote
  #3  
Old January 4th, 2022, 17:36
Unclewolverine Unclewolverine is offline
NAXJA Forum User
 
Join Date: Jun 2019
Location: Kansas
Posts: 749
Re: Fuel Pump Check Valve or leaky Injectors?

Yeah, exact symptoms described by sever others, solved by new injectors.
Reply With Quote
  #4  
Old January 5th, 2022, 07:48
Lost_Wrench Lost_Wrench is offline
NAXJA Forum User
 
Join Date: Dec 2020
Location: CO
Posts: 95
Re: Fuel Pump Check Valve or leaky Injectors?

Awesome thank you guys! I picked up a set of brand new (not used or refurbished) matched 4 hole injectors.
Reply With Quote
  #5  
Old January 6th, 2022, 04:09
cruiser54's Avatar
cruiser54 cruiser54 is offline
NAXJA Forum User
 
Join Date: Nov 2009
Location: Prescott, Az
Posts: 7,002
Re: Fuel Pump Check Valve or leaky Injectors?

Quote:
Originally Posted by Lost_Wrench View Post
Awesome thank you guys! I picked up a set of brand new (not used or refurbished) matched 4 hole injectors.
Hopefully they're not new Chinese injectors.....
Reply With Quote
  #6  
Old January 14th, 2022, 20:23
Evan_in_CA Evan_in_CA is offline
NAXJA Forum User
 
Join Date: Dec 2021
Location: Los Banos, CA
Posts: 10
Re: Fuel Pump Check Valve or leaky Injectors?

I had the long start issue, replaced the fuel pump assembly, then ended up with the same problem youre having. I guess maintaining fuel in the lines caused the injectors to leak into the cylinders. Replacing with new injectors fixed the issue for me.
Reply With Quote
  #7  
Old January 18th, 2022, 11:44
Lost_Wrench Lost_Wrench is offline
NAXJA Forum User
 
Join Date: Dec 2020
Location: CO
Posts: 95
Re: Fuel Pump Check Valve or leaky Injectors?

UPDATE: I replaced my injectors with a set if Bosch 4 hole injectors (serial # ending in 710) that cost me $60 total on EBay. The Jeep - which had been running fine with the old injectors but had long cranking time sympoms - ran like hell with those Bosch injectors. And i mean hell. Hard starting, rough idle, backfiring, stumbling. So I put the old original Chrysler injectors back in. It ran better but not the same as before. Running it down the highway it would bog down and then suddenly pick back up. Then it sat overnight. Now it runs like hell just like with the Bosch injectors.

I tested the fuel pressure on the rail today and it's at 30 psi. Apparently some 96 XJ's are supposed to run at 31 psi and at some point in 96 they went from a fuel rail mounted regulator to one attached to the actual fuel pump in the tank and that setup is supposed to run at like 49 psi. Seems like my pressure is low according to that, anyone have knowledge of this or a Chilton manual they could check for correct pressure for me? This Jeep does not have a fuel pressure regulator on the rail and my FP is not very old and maybe has 5k on it. Previous owner replaced the fuel tank, pump and filter, due to it having sat with old gas in it for too many years. I believe him I guess, the gas tank and fuel filter still look brand new.

Today I also bought new Standard Injectors from Oreilly for $300 total but I need to figure out if I have the correct fuel pressure before I install them for no reason. I'm perplexed at how swapping out injectors and resetting the pcm could suddenly make the Jeep run so terribly when it ran pretty great before, aside from the long cranking time to start (which only did so after it warmed up, it cold started right away every time). None of the injectors are leaking onto the manifold or anything. Could I have fouled the heck out of my plugs with those crappy bosches? Still no check engine light curiously. Well I'm really confused now, and rambling. Thanks for the responses thus far everyone!
Reply With Quote
  #8  
Old January 18th, 2022, 14:50
Lost_Wrench Lost_Wrench is offline
NAXJA Forum User
 
Join Date: Dec 2020
Location: CO
Posts: 95
Re: Fuel Pump Check Valve or leaky Injectors?

UPDATE: Just installed the new Standard Fuel Injectors and started the Jeep. Ran terribly again and the exhaust was super rich. I pulled all of the spark plugs and cylinder 2 was completely full of fuel, the electrode was even fully submerged it was so flooded. The other plugs all looked fine, no noticeable fouling that I could tell. I don't think the new Standard injector I just Installed in cylinder 2 is the issue because when I Installed the crappy Bosch injectors I could pull the wire harness off of the cylinder 2 injector and there was no difference in the way it idled. So something is up with cylinder 2 that's making it dump fuel in there.
Reply With Quote
  #9  
Old January 18th, 2022, 15:24
Lost_Wrench Lost_Wrench is offline
NAXJA Forum User
 
Join Date: Dec 2020
Location: CO
Posts: 95
Re: Fuel Pump Check Valve or leaky Injectors?

Here is what I've learned today.

1) Cylinder 2 is flooding badly
2) Cylinder 2 has a brand new fuel injector
3) Cylinder 2 has spark and a new champion plug

Why is cylinder 2 flooding even after I let it dry out?
Reply With Quote
  #10  
Old January 18th, 2022, 17:22
Unclewolverine Unclewolverine is offline
NAXJA Forum User
 
Join Date: Jun 2019
Location: Kansas
Posts: 749
Re: Fuel Pump Check Valve or leaky Injectors?

Switch that injector to another cylinder. If the flooding moves its the injector, if not there is a mechanical problem with the engine; valve not seating, bent pushrod, broken rocker, etc.
Reply With Quote
  #11  
Old January 18th, 2022, 17:55
Lost_Wrench Lost_Wrench is offline
NAXJA Forum User
 
Join Date: Dec 2020
Location: CO
Posts: 95
Re: Fuel Pump Check Valve or leaky Injectors?

Ok thanks, I'll do that tomorrow.

Any chance it could be an electrical issue such as a bad ground or the wires that go to that particular injector? When the engine is running and I unplug the wire harness from the cylinder 2 injector there is no change in the motor's idling or in the performance of the motor, it's like it doesn't exist even though it's getting air, fuel, and spark. The cylinder 2 injector meanwhile, is still dumping fuel despite being unplugged, which it shouldn't be right?
Reply With Quote
  #12  
Old January 18th, 2022, 20:54
DustyWagoneer's Avatar
DustyWagoneer DustyWagoneer is offline
NAXJA Forum User
 
Join Date: Feb 2018
Location: Outterlimits
Posts: 91
Re: Fuel Pump Check Valve or leaky Injectors?

Maybe try reseting your PCM??

https://youtu.be/Gj4G9_O4r9c
Reply With Quote
  #13  
Old January 19th, 2022, 09:41
Unclewolverine Unclewolverine is offline
NAXJA Forum User
 
Join Date: Jun 2019
Location: Kansas
Posts: 749
Re: Fuel Pump Check Valve or leaky Injectors?

That injector is bad. You unplug it nothing should be coming out.
Reply With Quote
  #14  
Old January 19th, 2022, 12:16
Lost_Wrench Lost_Wrench is offline
NAXJA Forum User
 
Join Date: Dec 2020
Location: CO
Posts: 95
Re: Fuel Pump Check Valve or leaky Injectors?

BAD NEWS! Today I reset the PCM..again. No change.

THEN I checked my oil, which looked fine at first glance but smelled kinda sweet and seemed "runny" so I took the oil filler cap off and looked at the underside of it and it's the dreaded milkshake. So looks like what happened is the head gasket failed and coolant was getting into cylinder 2 which is why it was so saturated and wouldn't fire normally despite having air + fuel + spark. Examining my exhaust and it was running really rich and dripping way too much out of the tailpipe leaving a small puddle every time.

Tracing this back to my original symptom though which was long cranking to get started and stumbling for a matter of seconds before giving it some gas, and I think the head gasket was already beginning to allow some coolant in, and the stumbling was that coolant getting cleared out of the cylinder. Once the engine sat for a long time it started right up but still stumbled a bunch so maybe whatever coolant was in there overnight evaporated some? When I changed out the injectors something must have happened to worsen the failed head gasket. Perhaps fresh injectors made better combustion and blew out the hole more, Idk. Thanks for all of your comments and help so far, I'll update as I make progress with my head gasket in the coming weeks.
Reply With Quote
  #15  
Old January 19th, 2022, 12:30
RCP Phx RCP Phx is offline
NAXJA Forum User
 
Join Date: Mar 2003
Location: Phoenix,Az
Posts: 15,753
Re: Fuel Pump Check Valve or leaky Injectors?

2 things, you never got a good set of injectors (I don't think so), if you think you did then you've got to do some major wiring checks.
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Fuel pump check valve DrMoab OEM Tech Discussion 11 July 18th, 2013 10:40
Fuel Pump and Check Valve Root Moose OEM Tech Discussion 11 March 27th, 2012 22:24
Fuel Pump Check valve tragiccomic1972 OEM Tech Discussion 9 April 27th, 2011 13:36
01 Xj Fuel Pump Check Valve Question CMK4425 OEM Tech Discussion 5 February 27th, 2011 16:25
Fuel pump check valve the_weirdo OEM Tech Discussion 1 February 23rd, 2011 20:38


All times are GMT -7. The time now is 05:40.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014